FIG. 1 shows a state of the art multiple-powersupply traction system capable of operating under single-phase AC or under DC voltage.
In order to deliver DC to the traction inverters 1, it is necessary under single-phase AC power 2 to use a transformer 3 whose secondary winding 4 is connected to an input AC/DC converter 5 feeding a common bus 6.
The common bus 6 delivers power to the traction inverters 1 and to other equipment of the train (not shown).
In general, the common bus 6 must possess large total capacitance in order to deliver a stabilized voltage to the traction inverters 1 which are voltage operated, with this applying under all degraded operating modes: sudden load shedding, loss of pantograph connection, etc.
The input single-phase AC/DC converter and rectifier 5 has an output capacitor 7.
In particular, single-phase AC/DC converter rectifiers built using IGBT components need a capacitor to be placed as close as possible in order to reduce cabling inductances.
When inputting DC power 8, the common bus 6 is either directly connected through switch 14 to a catenary 9 via a filter 10, or else it is powered via a DC/DC converter 11 that raises or lowers voltage.
While under DC power, the single-phase AC/DC converter rectifier 5 is conventionally isolated from the common bus 6 by opening an output contactor 12.
A drawback of such a prior art solution is that the multiple-powersupply traction system requires the use of an additional capacitor (not shown) while being powered under DC.